sparc: fixup for conversion to generic execve

sparc: fixup for conversion to generic execve

Fixes these errors:

arch/sparc/kernel/head_64.o: In function `sys64_execve':
(.text+0x1f58): relocation truncated to fit: R_SPARC_WDISP19 against symbol `sys_execve' defined in .text section in fs/built-in.o
arch/sparc/kernel/head_64.o: In function `sys32_execve':
(.text+0x1f64): relocation truncated to fit: R_SPARC_WDISP19 against symbol `compat_sys_execve' defined in .text section in fs/built-in.o

Dictated-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>