misc: rtsx: add missing write register handling

If an error occurs at the stage of working with registers in conjunction
with MCU_Block, it will not be processed.

The occurrence of errors at this stage may signal an impact on writes to
the device's PCI registers and is a more global problem than a
driver-level security problem, but adding a handler would be a good
practice.

Add a missing error handling.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c0e5f4e73a ("misc: rtsx: Add support for RTS5261")
Signed-off-by: Gleb Markov <markov.gi@npc-ksb.ru>
Link: https://patch.msgid.link/20260629130920.1260-1-markov.gi@npc-ksb.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/cardreader/rtsx_pcr.c

@@ -1196,6 +1196,8 @@ static int rtsx_pci_init_hw(struct rtsx_pcr *pcr)
 		/* Gating real mcu clock */
 		err = rtsx_pci_write_register(pcr, RTS5261_FW_CFG1,
 			RTS5261_MCU_CLOCK_GATING, 0);
+		if (err < 0)
+			return err;
 		err = rtsx_pci_write_register(pcr, RTS5261_REG_FPDCTL,
 			SSC_POWER_DOWN, 0);
 	} else {