tools/xenstored: Correct the prototype of domain_max_chk()

Some version of GCC will complain because the prototype and the
declaration of domain_max_chk() don't match:

xenstored_domain.c:1503:6: error: conflicting types for 'domain_max_chk' due to enum/integer mismatch; have '_Bool(const struct connection *, enum accitem,  unsigned int)' [-Werror=enum-int-mismatch]
 1503 | bool domain_max_chk(const struct connection *conn, enum accitem what,
      |      ^~~~~~~~~~~~~~
In file included from xenstored_domain.c:31:
xenstored_domain.h:146:6: note: previous declaration of 'domain_max_chk' with type '_Bool(const struct connection *, unsigned int,  unsigned int)'
  146 | bool domain_max_chk(const struct connection *conn, unsigned int what,
      |      ^~~~~~~~~~~~~~

Update the prototype to match the declaration.

This was spotted by Gitlab CI with the job opensuse-tumbleweed-gcc.

Fixes: 685048441e ("tools/xenstore: switch quota management to be table based")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
Tested-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

tools/xenstore/xenstored_domain.h

@@ -143,7 +143,7 @@ void acc_drop(struct connection *conn);
 void acc_commit(struct connection *conn);
 int domain_max_global_acc(const void *ctx, struct connection *conn);
 void domain_reset_global_acc(void);
-bool domain_max_chk(const struct connection *conn, unsigned int what,
+bool domain_max_chk(const struct connection *conn, enum accitem what,
 		    unsigned int val);
 
 extern long wrl_ntransactions;