spi/rtc-m41t93: Use spi_get_drvdata() for SPI devices

One new offender detected by the recently increased type checking in
platform_get_drvdata():

drivers/rtc/rtc-m41t93.c: In function ‘m41t93_remove’:
drivers/rtc/rtc-m41t93.c:192: warning: passing argument 1 of ‘platform_get_drvdata’ from incompatible pointer type

Use spi_get_drvdata() instead of platform_get_drvdata(), cfr. commit
42fea15d ("spi/rtc-{ds1390,ds3234,m41t94}:
Use spi_get_drvdata() for SPI devices")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/rtc/rtc-m41t93.c

@@ -189,7 +189,7 @@ static int __devinit m41t93_probe(struct spi_device *spi)
 
 static int __devexit m41t93_remove(struct spi_device *spi)
 {
-	struct rtc_device *rtc = platform_get_drvdata(spi);
+	struct rtc_device *rtc = spi_get_drvdata(spi);
 
 	if (rtc)
 		rtc_device_unregister(rtc);