video: fbdev: pvr2fb: fix build warning when compiling as module

Add missing #ifndef MODULE around pvr2_get_param_val().

Fixes: 0f5a5712 ("video: fbdev: pvr2fb: add COMPILE_TEST support")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>