linux-user/sh4: fix incorrect memory write

not hit since 2009! :)

linux-user/elfload.c:1102:20: warning: Out of bound memory access (access exceeds upper limit of memory block)
        (*regs[i]) = tswap32(env->gregs[i]);
        ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: Clang Static Analyzer
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
