staging: gpib: fmh: Drop residue from fmh_gpid_fifo_read_countable()

staging: gpib: fmh: Drop residue from fmh_gpid_fifo_read_countable()

Clang warns (or errors with CONFIG_WERROR=y):

  drivers/staging/gpib/fmh_gpib/fmh_gpib.c:970:43: error: variable 'residue' is uninitialized when used here [-Werror,-Wuninitialized]
    970 |                                 (int)(*bytes_read), (int)length, (int)residue);
        |                                                                       ^~~~~~~

residue is never initialized in this function and it is not used outside
of an error print. Just remove it altogether, as it is likely not
necessary in this function, as this same exact statement in present in
fmh_gpib_dma_read().

Fixes: 8e4841a0888c ("staging: gpib: Add Frank Mori Hess FPGA PCI GPIB driver")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20241015-staging-gpib-fmh-fix-residue-used-uninitialized-v1-1-23ef05b099da@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>