rtc: spacemit: handle regmap_test_bits() error return

rtc: spacemit: handle regmap_test_bits() error return

p1_rtc_read_time() called if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
to check if the RTC was enabled.

regmap_test_bits() returns 1 if the bit is set, 0 if not set, and a
negative error code (e.g. -EIO) if reading the control register fails.
Using !regmap_test_bits(...) evaluates a negative error code as boolean
false, causing I2C/regmap read failures to be ignored and incorrectly
proceeding to read time registers from a failing device.

Fix this by capturing the return value of regmap_test_bits() and returning
the error code if negative, or -EINVAL if the RTC is disabled.

Fixes: a6de182daa2b ("rtc: spacemit: support the SpacemiT P1 RTC")
Reviewed-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Surendra Singh Chouhan <kr494167@gmail.com>
Link: https://patch.msgid.link/20260724135803.81223-1-kr494167@gmail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>