staging: sm750fb: fix checkpatch warning architecture specific defines should be...

staging: sm750fb: fix checkpatch warning architecture specific defines should be avoided

Replace architecture-specific defines with CONFIG_X86 checks to improve
portability and adhere to kernel coding standards.

Fixes checkpatch warning:
- CHECK: architecture specific defines should be avoided.

Changes made:
- Using CONFIG_X86 instead of i386 and x86.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Michael Anckaert <michael.anckaert@gmail.com>
Link: https://lore.kernel.org/r/Z6x0GEM5sxcruYlS@michael-devbox
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>