rombios: Remove the use of egrep

As the Alpine 3.18 container notes:

  egrep: warning: egrep is obsolescent; using grep -E

Adjust it.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

tools/firmware/rombios/32bit/Makefile

@@ -26,7 +26,7 @@ $(TARGET): 32bitbios_all.o
 32bitbios_all.o: 32bitbios.o tcgbios/tcgbiosext.o util.o pmm.o
 	$(LD) $(LDFLAGS_DIRECT) -s -r $^ -o 32bitbios_all.o
 	@nm 32bitbios_all.o |                                \
-	  egrep '^ +U ' >/dev/null && {                      \
+	  grep -E '^ +U ' >/dev/null && {                    \
 	    echo "There are undefined symbols in the BIOS:"; \
 	    nm -u 32bitbios_all.o;                           \
 	    exit 11;                                         \