Fix multiple W=1 kernel-doc warnings in i2c-rk3x.c:

drivers/i2c/busses/i2c-rk3x.c:83: warning: missing initial short description on line:
 * struct i2c_spec_values:
drivers/i2c/busses/i2c-rk3x.c:139: warning: missing initial short description on line:
 * struct rk3x_i2c_calced_timings:
drivers/i2c/busses/i2c-rk3x.c:162: warning: missing initial short description on line:
 * struct rk3x_i2c_soc_data:
drivers/i2c/busses/i2c-rk3x.c:242: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Generate a START condition, which triggers a REG_INT_START interrupt.
drivers/i2c/busses/i2c-rk3x.c:261: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Generate a STOP condition, which triggers a REG_INT_STOP interrupt.
drivers/i2c/busses/i2c-rk3x.c:304: warning: expecting prototype for Setup a read according to i2c(). Prototype was for rk3x_i2c_prepare_read() instead
drivers/i2c/busses/i2c-rk3x.c:335: warning: expecting prototype for Fill the transmit buffer with data from i2c(). Prototype was for rk3x_i2c_fill_transmit_buf() instead
drivers/i2c/busses/i2c-rk3x.c:535: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Get timing values of I2C specification
drivers/i2c/busses/i2c-rk3x.c:552: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Calculate divider values for desired SCL frequency
drivers/i2c/busses/i2c-rk3x.c:713: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Calculate timing values for desired SCL frequency
drivers/i2c/busses/i2c-rk3x.c:963: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Setup I2C registers for an I2C operation specified by msgs, num.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>