libelf: avoid UB in elf_xen_feature_{get,set}()

When the left shift amount is up to 31, the shifted quantity wants to be
of unsigned int (or wider) type.

While there also adjust types: get doesn't alter the array and returns a
boolean, while both don't really accept negative "nr". Drop a stray
blank each as well.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>

xen/include/xen/libelf.h

@@ -445,13 +445,13 @@ struct elf_dom_parms {
     uint64_t virt_kend;
 };
 
-static inline void elf_xen_feature_set(int nr, uint32_t * addr)
+static inline void elf_xen_feature_set(unsigned int nr, uint32_t *addr)
 {
-    addr[nr >> 5] |= 1 << (nr & 31);
+    addr[nr >> 5] |= 1U << (nr & 31);
 }
-static inline int elf_xen_feature_get(int nr, uint32_t * addr)
+static inline bool elf_xen_feature_get(unsigned int nr, const uint32_t *addr)
 {
-    return !!(addr[nr >> 5] & (1 << (nr & 31)));
+    return addr[nr >> 5] & (1U << (nr & 31));
 }
 
 elf_errorstatus elf_xen_parse_features(const char *features,