kernel: fix linux/spi/spidev.h portability issues with musl

Felix will try to get this define included into musl

lede-commit: 795e7cf60de19e7a076a46874fab7bb88b43bbff
Signed-off-by: Felix Fietkau <nbd@nbd.name>

include/uapi/linux/spi/spidev.h

@@ -112,7 +112,7 @@ struct spi_ioc_transfer {
 
 /* not all platforms use <asm-generic/ioctl.h> or _IOC_TYPECHECK() ... */
 #define SPI_MSGSIZE(N) \
-	((((N)*(sizeof (struct spi_ioc_transfer))) < (1 << _IOC_SIZEBITS)) \
+	((((N)*(sizeof(struct spi_ioc_transfer))) < (1 << 13)) \
 		? ((N)*(sizeof (struct spi_ioc_transfer))) : 0)
 #define SPI_IOC_MESSAGE(N) _IOW(SPI_IOC_MAGIC, 0, char[SPI_MSGSIZE(N)])