Fix gdb build on hppa-linux

Fix gdb build on hppa-linux

Fixes:

  CXX    hppa-linux-nat.o
../../src/gdb/hppa-linux-nat.c:277:17: error: no 'void hppa_linux_nat_target::fetch_inferior_registers(regcache*, int)' member function declared in class 'hppa_linux_nat_target'
        int regno)
                 ^
../../src/gdb/hppa-linux-nat.c:224:1: error: 'void fetch_register(regcache*, int)' defined but not used [-Werror=unused-function]
 fetch_register (struct regcache *regcache, int regno)
 ^~~~~~~~~~~~~~

gdb/ChangeLog:

	* gdb/hppa-linux-nat.c
	(hppa_linux_nat_target::fetch_inferior_registers): Rename to
	hppa_linux_nat_target::fetch_registers.