bpf, docs: Fix the description of 'src' in ALU instructions

An ALU instruction's source operand can be the value in the source
register or the 32-bit immediate value encoded in the instruction. This
is controlled by the 's' bit of the 'opcode'.

The current description explicitly uses the phrase 'value of the source
register' when defining the meaning of 'src'.

Change the description to use 'source operand' in place of 'value of the
source register'.
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Dave Thaler <dthaler1968@gmail.com>
Link: https://lore.kernel.org/r/20240514130303.113607-1-puranjay@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/bpf/standardization/instruction-set.rst

@@ -301,8 +301,9 @@ Arithmetic instructions
 ``ALU`` uses 32-bit wide operands while ``ALU64`` uses 64-bit wide operands for
 otherwise identical operations. ``ALU64`` instructions belong to the
 base64 conformance group unless noted otherwise.
-The 'code' field encodes the operation as below, where 'src' and 'dst' refer
-to the values of the source and destination registers, respectively.
+The 'code' field encodes the operation as below, where 'src' refers to the
+the source operand and 'dst' refers to the value of the destination
+register.
 
 =====  =====  =======  ==========================================================
 name   code   offset   description