powerpc/fb: Call internal __phys_mem_access_prot() in fbdev code

Call __phys_mem_access_prot() from the fbdev mmap helper
pgprot_framebuffer(). Allows to avoid the file argument of NULL.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230922080636.26762-6-tzimmermann@suse.de

arch/powerpc/include/asm/fb.h

@@ -8,12 +8,7 @@ static inline pgprot_t pgprot_framebuffer(pgprot_t prot,
 					  unsigned long vm_start, unsigned long vm_end,
 					  unsigned long offset)
 {
-	/*
-	 * PowerPC's implementation of phys_mem_access_prot() does
-	 * not use the file argument. Set it to NULL in preparation
-	 * of later updates to the interface.
-	 */
-	return phys_mem_access_prot(NULL, PHYS_PFN(offset), vm_end - vm_start, prot);
+	return __phys_mem_access_prot(PHYS_PFN(offset), vm_end - vm_start, prot);
 }
 #define pgprot_framebuffer pgprot_framebuffer