i2c: busses: i2c-pnx: Provide descriptions for 'alg_data' data structure

Fixes the following W=1 kernel build warning(s):

 drivers/i2c/busses/i2c-pnx.c:147: warning: Function parameter or member 'alg_data' not described in 'i2c_pnx_start'
 drivers/i2c/busses/i2c-pnx.c:147: warning: Excess function parameter 'adap' description in 'i2c_pnx_start'
 drivers/i2c/busses/i2c-pnx.c:202: warning: Function parameter or member 'alg_data' not described in 'i2c_pnx_stop'
 drivers/i2c/busses/i2c-pnx.c:202: warning: Excess function parameter 'adap' description in 'i2c_pnx_stop'
 drivers/i2c/busses/i2c-pnx.c:231: warning: Function parameter or member 'alg_data' not described in 'i2c_pnx_master_xmit'
 drivers/i2c/busses/i2c-pnx.c:231: warning: Excess function parameter 'adap' description in 'i2c_pnx_master_xmit'
 drivers/i2c/busses/i2c-pnx.c:301: warning: Function parameter or member 'alg_data' not described in 'i2c_pnx_master_rcv'
 drivers/i2c/busses/i2c-pnx.c:301: warning: Excess function parameter 'adap' description in 'i2c_pnx_master_rcv'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>