dwc2/host: HFIR: Fix timing off-by-one

[maximevince]

Describe the PR
HFIR register for SOF timing was programmed with an off-by-one value (it needs a -1 applied).

• This probably comes from a historical error in the Synopsys databook. They corrected it in version 3.30a, according to this comment on a mailinglist: https://lists.infradead.org/pipermail/linux-rpi-kernel/2016-February/003290.html

• Also, the official Linux kernel dwc2 driver (maintained by Synopsys) contains the values with -1 offset, as can be seen in the dwc2_calc_frame_interval() function here:
  https://github.com/torvalds/linux/blob/900241a5cc15e6e0709a012051cc72d224cd6a6e/drivers/usb/dwc2/hcd.c#L326

@HiFiPhile @roma-jam

[HiFiPhile]

Thank you !

Hum that's interesting, on databook 4.20a the - 1 is still missing.

[maximevince]

Huh! I don't have access to their databook(s), unfortunately. So I just copied the mentioned versions from the mailing list thread!