staging: rts5139: Make variables inside #ifdef CONFIG_PM

If CONFIG_PM=n:

drivers/staging/rts5139/rts51x_transport.c:649: warning: ‘media_not_present’ defined but not used
drivers/staging/rts5139/rts51x_transport.c:651: warning: ‘invalid_cmd_field’ defined but not used

Move the variables inside the #ifdef CONFIG_PM, and make them const while
we're at it.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>