serial: sc16is7xx: convert from _raw_ to _noinc_ regmap functions for FIFO

In the Linux kernel, the following vulnerability has been resolved:

serial: sc16is7xx: convert from _raw_ to _noinc_ regmap functions for FIFO

The SC16IS7XX IC supports a burst mode to access the FIFOs where the

initial register address is sent ($00), followed by all the FIFO data

without having to resend the register address each time. In this mode, the

IC doesn't increment the register address for each R/W byte.

The regmap_raw_read() and regmap_raw_write() are functions which can

perform IO over multiple registers. They are currently used to read/write

from/to the FIFO, and although they operate correctly in this burst mode on

the SPI bus, they would corrupt the regmap cache if it was not disabled

manually. The reason is that when the R/W size is more than 1 byte, these

functions assume that the register address is incremented and handle the

cache accordingly.

Convert FIFO R/W functions to use the regmap _noinc_ versions in order to

remove the manual cache control which was a workaround when using the

_raw_ versions. FIFO registers are properly declared as volatile so

cache will not be used/updated for FIFO accesses.